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Blueprint for Survival
Ensuring a future for Florida's native flora
by Vivian Negrón-Ortiz and David Bender
Photo Credit: Bok Tower Garden
The southeastern United States is home to a large number of plant species that occur only in this region, and nowhere else in the world. Approximately 385 species are restricted to "La Florida" alone, which truly is "covered with flowers!" Many of these species are now threatened by urbanization, habitat conversion, invasive species, fire suppression, and alteration of natural fire regimes. Each carries a genetic blueprint, which holds the key to the ability of populations and species to persist over evolutionary time through changing environments.
With this blueprint, botanists are better able to select the best combination of recovery actions that serve as the most efficient and effective way to recover endangered and threatened plant species.
Drs. Jim Hamrick and Dorset Trapnell of the University of Georgia recently discovered that Telephus spurge (Euphorbia telephioides), a member of the spurge family that is restricted to three counties in the Florida panhandle, maintains high levels of genetic diversity, within and among populations, relative to other plant species. This information sheds light into establishing new populations or augmenting existing ones, and suggesting populations for protection.
For instance, to augment or restore populations of Telephus spurge, propagules from the three most genetically dissimilar populations identified should be used. To preserve this threatened species' overall genetic diversity, five main populations – out of the 40 locations known to date – should be prioritized. At present four populations are secured and well-managed, with an ex-situ, or off-site, seed collection maintained at the Rare Plant Conservation Program of Bok Tower Gardens, Florida.
In contrast, Florida ziziphus(Ziziphus celata), an endangered shrub narrowly constrained to extremely dry soils on the Lake Wales Ridge in central Florida, possess low genetic diversity. The 14 remaining wild populations may include as few as 30 distinct individuals, meaning that many of the individual shrubs may actually be clones. In fact, all shrubs in five populations are thought to belong to a single genetic individual. In many plant species, two genetically similar individuals cannot successfully produce seeds. This information is critical to enhance seed production and germination, since no evidence of natural seedling recruitment has been observed. For Florida ziziphus, research has revealed that seed production requires not only two different genetic individuals, but two compatible mating types. The study revealed three cross-compatible mating types. Since 2002, staff from the Archbold Biological Station, an independent, not-for-profit research institution in central Florida, carried out five experimental introductions and three augmentations of pre-existing single clonal populations. These efforts have resulted in high annual survival and modest seedling recruitment from introduced seeds. One population has flowered and set fruit.
Photo Credit: USFWS
Low genetic diversity was also observed in Miccosukee gooseberry(Ribes echinellum), a threatened shrub known from only two areas: one in Florida and one in South Carolina. This gooseberry reproduces both by clonal growth and by seed production. However, germination appears to be limited, and several off-site germination attempts have failed. Drs. Nora Oleas and Eric von Wettberg of Florida International University and the U.S. Fish and Wildlife Service (Service) found that the two known populations are composed of genetically distinct individuals—from a sample of 110 plants, 66 genotypes were found. Recently, the Service tested whether viable seeds can be produced by cross-pollinating genetically distinct individuals. Preliminary research suggests crosses between individuals from the Florida and South Carolina populations do enhance seed production. Additional research will be carried out to guide management actions of this species in Florida.
Understanding the genetic blueprint has improved the recovery prospects of these three plant species. For Florida ziziphus and Miccosukee gooseberry, the lack of germination,or seed viability, means that once established individuals die, the population cannot persist. Therefore, finding different or compatible genotypes is critical to maintain sexual reproduction. In contrast, species with more genetic variation, such as Telephus spurge, are more likely to tolerate a new stress or a changed environment. Because of its genetic diversity, Telephus spurge has a good chance of recovery.
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Vivian Negrón-Ortiz, a botanist in the Service's Panama City Field Office, can be reached at firstname.lastname@example.org or 850-769-0552, ext. 231. David Bender, a botanist in the Service's South Florida Ecological Services Field Office in Vero Beach, Florida, can be reached at email@example.com or 772-562-3909.
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